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The radiation directivity of a complicated conformal array of underwater acoustic transducers is presented based on the boundary "element method. It includes the element directivity of each transducer, the natural beam pattern and the controlled beam pattern of the transducer array. At first, the boundary element model of the conformal array is built up, and then the boundary condition is exerted on the model according to the design and environment in which the transducer array is used, and the radiation directivity of the conformal array is calculated. An experiment has been done to measure the directivity in an anechoic water tank. The calculated and the experimental results are compared and analyzed. They are consistent to each other. It is shown that the boundary element method together with the detailed calculations is successful to simulate and predict the radiation directivity of an underwater acoustic transducer array. 相似文献
33.
Dual-wavelength distributed Bragg reflector semiconductor laser based on a composite resonant cavity 下载免费PDF全文
We report a monolithic integrated dual-wavelength laser diode based on a distributed Bragg reflector (DBR) composite resonant cavity. The device consists of three sections, a DBR grating section, a passive phase section, and an active gain section. The gain section facet is cleaved to work as a laser cavity mirror. The other laser mirror is the DBR grating, which also functions as a wavelength filter and can control the number of wavelengths involved in the laser action. The reflection bandwidth of the DBR grating is fabricated to have an appropriate value to make the device work at the dual-wavelength lasing state. We adopt the quantum well intermixing (QWI) technique to provide low-absorption loss grating and passive phase section in the fabrication process. By tuning the injection currents on the DBR and the gain sections, the device can generate 0.596 nm-spaced dual-wavelength lasing at room temperature. 相似文献
34.
基于激光加载的材料状态方程的实验研究对靶面光强分布的均匀性及稳定性提出了极高的要求,靶面光强的上述两大特性在很大程度上决定了实验结果的精度和可重复性.本文针对传统窄带高相干激光装置在激光加载材料状态方程实验中表现出的靶面光强均匀性和光强分布稳定性两方面可能存在的问题,提出了基于宽带低相干激光,利用消衍射阵列透镜联合诱导非相干技术的束匀滑方案,并重点分析了波前相位畸变对靶面不均匀性及稳定性的影响.模拟结果表明,该方法明显降低了靶面不均匀性,提高了对波前相位畸变的包容度,获得了均匀、稳定的光强分布.统计分析显示,焦斑强度分布极差和不均匀性与波前相位畸变均方根梯度相关性较强.因此,可以根据统计结果以及实验对焦斑强度分布的要求,给出波前相位畸变的容差范围,对状态方程实验中激光驱动器参数的设计与优化具有指导意义. 相似文献
35.
Propagation of phase-locked partially coherent flattened beam array in turbulent atmosphere 总被引:2,自引:0,他引:2
Analytical formulae for phase-locked partially coherent flattened beam array propagating in a turbulent atmosphere are derived based on the extended Huygens–Fresnel principle. Beam propagation factor (BPF) is introduced to evaluate the beam quality at the receiving plane. The influence of beam order, transverse coherence width length and the intensity of turbulence is discussed in detail. 相似文献
36.
文章简要介绍了“数字信号处理”与“数字信号处理器(DSP)”的发展历史.在数字信号处理的应用中,实时实现是非常重要的,而DSP在实时处理中,扮演了一个重要的角色.文章中还介绍了DSP在实际应用中的一些关键技术,例如DSP的种类和选型,DSP的开发工具,实时软件的开发过程等.最后,还介绍了一些DSP的应用实例,如语音编码器,视频电话和视频会议系统,用于雷达和声纳的DSP并行处理系统 相似文献
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The recent expansion of French tram networks and the related local residential complaints mean that a better knowledge of the situations leading to negative reactions from the local inhabitants is required. Hence a research project has been conducted to evaluate and describe noise and vibration emission of trams as well as the perception by the local residents. This paper investigates tram noise emission on common straight track sections, involving two vehicle scales. First the acoustic power and the mean vertical directivity of the total tramset is assessed using an arc of microphones. Then the localisation and the analysis of the main noise sources are performed by means of a cross array during the tram pass-by. Two tram types representing two generations of French rolling stock, both running on two sites with distinct track characteristics, have been investigated considering the effect of speed, tram type, and track type on the noise source contributions and spectral features. Most sources are located in the lower part of the trams, mainly related to rolling noise, with a strong dependence on speed and track type. The tram type dependency, although globally of second importance, influences greatly the noise spectral distribution and behaviour. The HVAC was the only roof-mounted source which could be detected; its contribution towards building storeys becomes significant in configurations of low rolling noise. A tram noise emission model based on the various noise sources has been developed. 相似文献
39.
利用“神光-Ⅱ”的3路基频光输出及小透镜列阵束匀滑技术,通过优化设计和合理地选择光路组合,实现了多路叠加斜入射的驱动激光, 在靶材料中产生一个650~750μm范围内平面性良好的冲击波,有效地提高了“神光-Ⅱ”输出光束的利用率。同时,利用斜面靶进行的冲击稳定性实验表明,在靶面功率密度分别为3.26×1014及2.56×1014W/cm2时,冲击波至少在28.38~55.82和22.13~35.07μm的Al样品厚度内是稳定传播的。 相似文献
40.